Telnet: enable config option in TelnetLibrary for python telnetlib

To be able to change the logging behavior of the underlying python
telnetlib a new parameter is added in the open connection keyword.

Signed-off-by: Heiko Thiery <heiko.thiery@kontron.com>
You're right this is not needed. I used the code from the present _set_dafault_log_level method as reference. Therefore I think this check on this method is also needless. Please correct me if I'm wrong.